Transient receptor potential (TRP) channels are non-selective cation channels that are activated by a variety of stimuli. Numerous members of the ion channel family have been identified to date, including the cold-menthol receptor, also called TRPM8 (McKemy D. D., et al., Nature 2002, 416(6876), 52-58). Collectively, the TRP channels and related TRP-like receptors connote sensory responsivity to the entire continuum of thermal stimulation, selectively responding to threshold temperatures ranging from noxious hot through noxious cold as well as to certain chemicals that mimic these sensations. Specifically, TRPM8 is known to be stimulated by cool to cold temperatures as well as by chemical agents such as menthol and icilin, which may be responsible for the therapeutic cooling sensation that these agents provoke.
TRPM8 is located on primary nociceptive neurons (A-δ and C-fibers) and is also modulated by inflammation-mediated second messenger signals (Abe, J., et al., Neurosci Lett 2006, 397(1-2), 140-144; Premkumar, L. S., et al., J. Neurosci, 2005, 25(49), 11322-11329). The localization of TRPM8 on both A-δ and C-fibers may provide a basis for abnormal cold sensitivity in pathologic conditions wherein these neurons are altered, resulting in pain, often of a burning nature (Kobayashi, K., et al., J Comp Neurol, 2005, 493(4), 596-606; Roza, C., et al., Pain, 2006, 120(1-2), 24-35; and Xing, H., et al., J Neurophysiol, 2006, 95(2), 1221-30). Cold intolerance and paradoxical burning sensations induced by chemical or thermal cooling closely parallel symptoms seen in a wide range of clinical disorders and thus provide a strong rationale for the development of TRPM8 modulators as novel antihyperalgesic or antiallodynic agents. TRPM8 is also known to be expressed in brain, lung, bladder, gastrointestinal tract, blood vessels, prostate and immune cells, thereby providing the possibility for therapeutic modulation in a wide range of maladies.
There is a need in the art for TRPM8 antagonists that can be used to treat a disease, syndrome, or condition in a mammal in which the disease, syndrome, or condition is affected by the modulation of TRPM8 channels, such as pain, the diseases that lead to such pain, and pulmonary or vascular dysfunction.